1. Merck Index (in paper; an encyclopedia of chemicals, drugs, and biologicals; within the entry for a chemical, there may be references to articles and other publications describing how that chemical can be synthesized or prepared; contains indexes arranged by Registry Number, molecular formula, chemical name, etc.)
Dictionary of Organic Compounds (and supplements; in paper; within the entry for a chemical, there may be references to articles and other publications describing how that chemical can be synthesized or prepared)
Dictionary of Inorganic Compounds (and supplements; in paper; within the entry for a chemical, there may be references to articles and other publications describing how that chemical can be synthesized or prepared)
2. Organic Syntheses (in paper; use the Collective Volumes first--especially the index that covers the Collective Volumes; descriptions of preferred methods for preparing/synthesizing chemical substances)
3. CrossFire Beilstein (online; for organic compounds only)
4. Chemical Abstracts (online; search Chemical Abstracts via SciFinder Scholar or STN to locate journal articles and other publications describing the synthesis/preparation of a chemical substance)
